Ambulatory oxygen concentrator containing a three phase vacuum separation system

ABSTRACT

An oxygen concentrator comprises an oxygen reservoir and adsorbent columns that each have an inlet, an outlet, and a bed of adsorbent material. The concentrator also comprises an air inlet, an exhaust outlet, and a vacuum pump for pumping nitrogen rich gas from one of the column inlets to the exhaust outlet. A product control pump pumps oxygen rich gas from one of the column outlets to the oxygen reservoir. A control valve controls flow in and out of the columns by selectively connecting the air inlet to one column inlet, connecting the vacuum pump to another column inlet, and connecting the product control pump to a column outlet. A motor drives the vacuum pump and control valve to produce vacuum swing adsorption (VSA) cycles in which oxygen-rich product gas is separated and accumulated in the reservoir.

CROSS-REFERENCE TO RELATED APPLICATION(S)

Reference is hereby made to the following copending applications, whichwere filed on even date with the present application: “Ambulatory OxygenConcentrator Containing a Power Pack”, Theodore W. Jagger et al.,application Ser. No. ______; “Adsorbent Cartridge for OxygenConcentrator”, Theodore W. Jagger et al., application Ser. No. ______;“Personal Oxygen Concentrator”, Theodore W. Jagger et al., applicationSer. No. ______; “Method of Providing Ambulatory Oxygen”, Theodore W.Jagger et al., application Ser. No. ______; “Low Power Ambulatory OxygenConcentrator”, Theodore W. Jagger et al., application Ser. No. ______;“Ambulatory Oxygen Concentrator With High Efficiency Adsorbent”,Theodore W. Jagger et al., application Ser. No. ______; “Portable OxygenConcentrator With a Docking Station”, Theodore W. Jagger et al.,application Ser. No. ______; “Method of Controlling the Rate of OxygenProduced by an Oxygen Concentrator”, Theodore W. Jagger et al.,application Ser. No. ______; “Product Pump for an Oxygen Concentrator”,Theodore W. Jagger et al., application Ser. No. ______; and “Method andApparatus for Controlling the Purity of Oxygen Produced by an OxygenConcentrator”, Theodore W. Jagger et al., application Ser. No. ______.

BACKGROUND OF THE INVENTION

The field of this invention relates to oxygen concentrators. Inparticular, the invention relates to wearable oxygen concentrationsystems utilizing vacuum swing adsorption for creating an oxygen streamfor ambulatory respiratory patients.

There is a need for home and ambulatory oxygen systems for use bypatients. Supplemental oxygen is required for patients exhibitingsymptoms from certain diseases and lung disorders; for example,pulmonary fibrosis, sarcoidosis, or occupational lung disease. For suchpatients, oxygen therapy is an increasingly beneficial prescription tohelp the patients live normal and productive lives. While not a cure forlung disease, prescriptive supplemental oxygen increases bloodoxygenation, which reverses hypoxemia. Oxygen prescriptions preventlong-term effects of oxygen deficiency on organ systems, the heart,brain and kidneys. Oxygen treatment is also prescribed for ChronicObstructive Pulmonary Disease (COPD), heart disease, AIDS, asthma, andemphysema.

Currently, supplemental medical oxygen for therapy is provided to apatient from high pressure gas cylinders; cryogenic liquid invacuum-insulated containers or thermos bottles commonly called “dewars”,and oxygen concentrators. Some patients require in-home oxygen only,while others require in-home as well as ambulatory oxygen depending onthe prescription. The three systems are all used for in-home use.However, oxygen concentrators provide a special beneficial advantagebecause they do not require refilling of dewars or exchange of emptycylinders with full ones. Home oxygen concentrators, however, do havedrawbacks. They consume relatively large amounts of electricity; arerelatively large and heavy; emit excessive heat and are relativelynoisy.

There has been a need for an improved portable device for supplyingoxygen to a patient. Only small high pressure gas bottles and smallliquid dewars are truly portable enough to be used for ambulatory needs.Either system may be used for both in-home and ambulatory use. A patientusing a stationary oxygen system at home (or even a portable systemwhich cannot be readily transported), who travels must opt for smallcylinders towed in a wheeled stroller or for portable containers thatthey carry, typically on a shoulder sling. Both of these options havesignificant drawbacks.

A major drawback of the cylinder option is that small cylinders onlyprovide oxygen for a short duration. Moreover, these cylinders aremaintained at a high pressure, and thus their use is restricted due tosafety considerations. Another drawback of the cylinders is the refillrequirement after depletion of the contents of the cylinder. Emptycylinders must be refilled at specialized facilities, or in thepatient's home using a commercial oxygen concentrator which extractsoxygen from the air. The latter option requires an on-site compressor toboost the output pressure of the concentrator to meet cylinder refillpressure requirements. Filling of cylinders with oxygen in the home ispotentially dangerous due to the physics involved with compressing gas.Another detriment to cylinder usage is fire hazards associated withstorage of large volumes of oxygen in the home environment.

Convenience and safety issues are not the only drawbacks associated withthe use of cylinders. Another drawback is the cost associated withcylinders. Cylinders require special care, and specialized materials arerequired for high pressure oxygen compatibility, which in turn drives upthe cost of cylinder-based systems.

The liquid oxygen storage system also has drawbacks. The primarydrawback is the requirement of a base reservoir which necessitatesrefilling once a week or more from an outside source. Liquid oxygen istransferred from the base unit to a portable dewar, which is used by anambulatory patient. However, there is substantial waste, as a certainamount of oxygen is lost during the transfer to the portable containersand from evaporation. Up to twenty percent of the contents of the basecylinder is lost in the course of two weeks because of losses intransfers and normal evaporation. Even without withdrawal by thepatient, the base reservoir will typically boil dry over a period of oneto two months.

The aforementioned systems all require a refilling station. When thepatient is out in public, such stations are not readily available. Uponrunning low (or out) of oxygen, the patient must return home to aspecified place that can refill the system. Such a requirement detractsfrom the ambulatory usefulness of the systems.

The industry has developed a set of recommendations for systems targetedto provide portable oxygen for ambulatory patients. The Fifth OxygenConsensus Conference set forth the following standards for long-termoxygen therapy ambulatory equipment: 1) equipment must weigh less than10 lbs., 2) equipment must provide the equivalent of 2 liter/min ofcontinuous flow O₂, and 3) the flow rate must be maintained for fourhours or more. Thus, ambulatory equipment, or personal oxygen systems(POS), are to be inconspicuous to the public as well as unrestricting tothe patient. Cylinders and other liquid oxygen systems tend to be bulky,which interferes with normal daily activities. Similarly, cylinders andliquid oxygen systems are difficult to conceal from public view.Ideally, a POS is small, lightweight, quiet, and flexible which allowsthe device to be concealed from the public. The present invention,whereby oxygen rich gas is provided to a patient from a wearable oxygenconcentrator, meets and exceeds these standards.

BRIEF SUMMARY OF THE INVENTION

An oxygen concentrator includes an oxygen reservoir, adsorbent columnsthat each have a bed of adsorbent material, a vacuum pump for pumpingnitrogen rich gas from the columns to an exhaust, and a product controlpump which pumps product gas from the columns to a reservoir. A controlvalve controls flow in and out of the columns. A motor drives the vacuumpump and control valve to produce vacuum swing adsorption (VSA) cyclesin which oxygen-rich product gas is separated and accumulated in thereservoir.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a patient carrying the oxygen concentrator ofthe present invention.

FIG. 2 is a front perspective view of the oxygen concentrator.

FIG. 3 is a rear perspective view of the oxygen concentrator.

FIG. 4 is a front perspective view of the oxygen concentrator and adocking station.

FIG. 5 is a block diagram showing the components and connections of theoxygen concentrator.

FIG. 6 is a diagram showing rotary valve timing.

FIG. 7 is an exploded view of the oxygen concentrator in which the powerpack and the adsorbent cartridge have been removed.

FIG. 8 is a perspective view of the oxygen concentrator with a portionof the belt removed.

FIG. 9 is a perspective view of the components of the oxygenconcentrator without the belt.

FIG. 10 is a perspective view of the components contained within thecase portions of the modules and their associated pneumatic andelectrical connections of the oxygen concentrator.

FIG. 11 is a perspective view of the components contained within abattery module.

FIG. 12 a is a perspective view of an accumulator.

FIG. 12 b is a top view of the accumulator.

FIG. 12 c is a sectional view of the accumulator.

FIG. 12 d is another sectional view of the accumulator.

FIG. 13 is a perspective view of a control module.

FIG. 14 is a front view of the interior components of the controlmodule.

FIG. 15 is a perspective view of the cartridge contained within acartridge module.

FIG. 16 is an exploded view of columns and filters within the cartridge.

FIG. 17 is a rear perspective view of the oxygen concentrator and thedocking station.

FIG. 18 is a front perspective view of the docking station.

FIG. 19 is a chart showing the adsorption isotherms for two differentadsorbent materials.

DETAILED DESCRIPTION

The current invention relates to separation of gases using vacuum swingadsorption. Specifically, disclosed is an oxygen concentrator for apatient who requires a source of oxygen. The present invention isfurther explained with reference to the drawn figures in which likestructures are referred to by like numerals throughout the severalviews.

Overview—Oxygen Concentrator 100 (FIGS. 1-4)

FIG. 1 is a front view showing patient P with oxygen concentrator 100and oxygen delivery tube 102. Oxygen concentrator 100 is a small unitwhich utilizes vacuum swing adsorption to separate oxygen from theambient air around patient P. Oxygen concentrator 100 is compact andlight so as not to interfere with the ambulatory movement of patient P,and can produce a product stream of gas containing a range ofeighty-five to ninety-five percent oxygen.

Oxygen delivery tube 102 is a polymer tube or similar oxidationresistant structure, which extends from oxygen concentrator 100 to thenose, mouth, or port into the upper airway of patient P. Tube 102 allowsdelivery of oxygen to patient P for inhalation. In FIG. 1, patient P isabout six foot tall to illustrate an approximation of the relative sizeof oxygen concentrator 100.

FIG. 2 is a perspective view of oxygen concentrator 100. Oxygenconcentrator 100 is comprised of belt 104, power module 106 containingpower pack 108, reservoir module 110, control module 112 containing userinterface 114, and separation cartridge module 116. Oxygen concentrator100 is a portable oxygen separator used to provide an oxygen rich gasstream to patient P. Belt 104 connects and carries the modules 106, 110,112, and 116 of oxygen concentrator 100. Belt 104 may contain belt loops(not illustrated), clips, or a pair of straps that contain a buckle andholes or like fastening device for securing oxygen concentrator 100 topatient P. Alternatively, oxygen concentrator 100 may be placed in apurse, fanny pack, or similar personal carrying device for transportwith patient P.

Power module 106 provides the necessary power to operate the systems ofoxygen concentrator 100. In the embodiment illustrated, power module 106contains replaceable power pack 108. Reservoir module 110 stores oxygenrich gas that has been separated from ambient air by cartridge module116. Control module 112 pilots and regulates the interaction of thepower module 106, reservoir module 110, and separation cartridge module116 of oxygen concentrator 100. User interface 114 on control module 112is a console which allows patient P to adjust and monitor oxygenconcentrator 100.

FIG. 3 is a perspective view of the opposite side of oxygen concentrator100 as shown in FIG. 2. Illustrated in FIG. 3 are belt 104, power module106, reservoir module 110, control module 112, and separation cartridgemodule 116. Belt 104 is constructed to contain belt segments 120 formedby serrations 118. This allows the belt 104 to be flexible and conformto patient P's body while wearing oxygen concentrator 100. Belt 104 isfabricated from a flexible material, such as textile or plastic andcontains an inner padding such as foam. Belt 104 also houses theelectrical and pneumatic connections of oxygen concentrator 100.

FIG. 4 is a perspective view of the front side of the oxygenconcentrator 100 on docking station 122. Illustrated are oxygenconcentrator 100 comprising belt 104, power module 106, reservoir module110, control module 112, and separation cartridge module 116, along withdocking station 122 containing power pack chargers 124 a and 124 b. Belt104 is flexible and thus rests on the arc shaped docking station 122.Docking station 122 contains power pack chargers 124 a (with power pack108 a inserted therein) and 124 b, as well as concentrator dock 126which supports the oxygen concentrator 100 while on the docking station122. Docking station 122 converts AC power to recharge power packs 108.

Oxygen Concentrator 100 System Components and Connections (FIG. 5)

FIG. 5 is a block diagram of oxygen concentrator 100 illustrating powermodule 106, reservoir module 110, control module 112, and separationcartridge module 116, along with docking station 122 and showing thecomponents and connections among the modules and docking station 122.Oxygen concentrator 100 components includes product gas outlet port 103,adsorbent columns 130 a-130 c (each containing a respective inlet port132 a-132 c and a respective outlet port 134 a-134 c), air inlet port135, air inlet filter 136, product gas final filter 138, main valve 140,drive reducer 142, vacuum pump 144, drive 146, electric control module(ECM) 148, breakthrough flow sensor 150, valve position sensor 152,product control pump 154, check valve 156, main storage reservoir 158containing pressure sensor 159, dispensing valve 160, as well aspreviously identified components tubing 102, power pack 108, userinterface 114, and docking station 122.

As shown in FIG. 5, adsorbent cartridge module 116 includes adsorbentcolumns 130 a-130 c each containing respective inlet ports 132 a-132 cand outlet ports 134 a-134 c, air inlet filter 136, and product gasfinal filter 138. Ambient air enters air inlet port 135, passes throughair inlet filter 136, and enters valve 140 for distribution to adsorbentcolumns 130 a-130 c. Product gas passes through final filter 138 andproduct gas outlet port 103 into tubing 102 for delivery to patient P.Inlet ports 132 a-132 c of adsorbent columns 130 a-130 c connect tovalve 140 through inlet lines 164 a-164 c. Similarly, outlet ports 134a-134 c connect to valve 140 through outlet lines 166 a-166 c.

Control module 112 houses main valve 140, drive reducer 142, vacuum pump144, drive 146, electric control module (ECM) 148, breakthrough flowsensor 150, valve position sensor 152, and contains user interface 114.Main valve 140 is pneumatically connected to adsorbent columns 130 a-130c, as well as inlet filter 136 via inlet line 168, vacuum pump 144 viavacuum inlet line 170, product control pump 154 via vacuum line 172 andproduct gas line 174, and main reservoir 158 via product gas line 176.Valve 140 is actuated by drive 146 through a motor speed reducer 142.Also, valve 140 connects to breakthrough flow sensor 150 and valveposition sensor 152 which send electrical inputs 178 and 180 to ECM 148.

ECM 148 is a logic control, such as a PLC (programmable logiccontroller), microprocessor, or similar structure which controlsoperation of oxygen concentrator 100. ECM 148 contains the set of inputsand outputs associated with the modules for regulating oxygenconcentrator 100. ECM 148 also receives control setting inputs 182 and184 from user interface 114, and docking station 122, respectively,power pack management input 186 from power pack 108, reservoir pressureinput 188 from pressure sensor 159 in main reservoir 158, and nasalpressure input 190 from dispensing valve 160. ECM 148 provides interfaceoutput 192 to the user interface 114, interface output 194 to dockingstation 122, power management output 196 to power pack 108, dispensingvalve time open output 198 to dispensing valve 160, and motor driveoutput 200 to drive 146.

User interface 114 contains physical controls such as dials, toggleswitches, push button switches, and similar controls, for operatingoxygen concentrator 100. The physical controls provide electricalcontrol settings to ECM 148. ECM 148 reads these settings as inputs 182and provides output 192 to the user interface 114. The status isconverted from electric signals to physical output by indicator lights,status display, and similar structures of user interface 114.

Power pack management input 186 and output 196 control the charge anddischarge of voltage from power pack 108 to drive 146 via ECM 148. Drive146 will activate vacuum pump 144, valve 140 through drive speed reducer142, and any other systems requiring power. Power pack management output196 will also supply power to indicator lights, status display, audiblealarm (if included), and other passive electrical system requirements onuser interface 114 through ECM 148.

ECM 148 controls and coordinates the steps of the vacuum swingadsorption cycle through its inputs and outputs. In one embodiment,breakthrough flow sensor 150 provides an input 178 into ECM 148 bymeasuring air flow rates. The position of valve 140 is detected by valveposition sensor 152 to produce input 180. Reservoir 158 contains asensor to produce reservoir pressure input 188. Dispensing valve 160also contains a pressure sensor which provides nasal pressure input 190in response to differential pressure. ECM 148 reads these inputs tocontrol the cycle by changing outputs, such as motor drive output 200for drive 146. Drive 146 propels vacuum pump 144. Vacuum pump 144creates a vacuum that is communicated to valve 140 through vacuum inputline 170, while dispelling nitrogen rich gas as exhaust 177. Anotheroutput 198 controls the time that dispensing valve 160 is open. In thisembodiment, the inputs and outputs are connected to a PLC within ECM 148which is programmed to control the cycle of oxygen concentrator 100.

Contained within reservoir module 110 is an oxygen-rich gas accumulatorcomprising reservoir 158, check valve 156, product control pump 154, andcheck valve 153. Reservoir 158 receives oxygen-rich gas produced byoxygen concentrator 100 and stores it at a low pressure above ambientuntil it is required for use. A portion of the stored oxygen-rich gas isdelivered back to valve 140 by product gas line 176 for use in orderingthe nitrogen content in adsorbent columns 130 a-130 c by moving much ofthe residual nitrogen held after evacuation near the outlets 134 a-134 ctoward inlets 132 a-132 c of the columns 1130 a-130 c. Reservoir 158 isin communication with dispensing valve 160 through product gas line 202.Check valve 156 opens to allow oxygen into reservoir 158 and closes toprevent backflow of oxygen upon reaching the desired pressure inreservoir 158.

Product control pump 154 is driven by vacuum provided by the vacuum pump144 through valve 140 via vacuum line 172. Product line 174 is incommunication from separation cartridge module 116 to check valve 153,which opens to allow product control pump 154 to transport separatedoxygen-rich gas to reservoir 158. Product control pump 154 delivers theproduct gas to main reservoir 158 through check valve 156.

Dispensing valve 160 and power pack 108 are contained within powermodule 106. Dispensing valve 160 is used to feed the flow of oxygen-richgas to the patient P by delivery of the product gas through finalproduct gas line 205 to product final filter 138. The product gas isobtained from the main reservoir 158 through product gas line 202. Powerpack 108 provides the power supply for oxygen concentrator 100 aspreviously described. Power pack 108 is rechargeable through dockingstation 122 as represented by power connection 204.

Vacuum Swing Adsorption (VSA) Process—Overview

Oxygen concentrator 100 operates using a vacuum swing adsorptionprocess, which involves a series of cycles that include a feed step orphase, an evacuation step or phase, and a repressurization step orphase. Each of these three phases takes place in one of the threecolumns 130 a-130 c at any given time. Each column 130 a-130 c is in adifferent phase. For purposes of explanation, the VSA process will bedescribed in reference to “column 130”, which is representative of eachof the three columns 130 a-130 c.

In the feed phase, a gas stream of ambient air 162 enters inlet end 132of column 130 while product gas containing concentrated oxygen isdelivered from outlet end 134 of column 130. The slight vacuum in column130 draws air 162 into column 130 and through an adsorbent material(typically a zeolite) which preferentially retains specific componentsof air (nitrogen), allowing the desired product (oxygen) to passthrough. A mass transfer zone (MTZ), which is a small region in whichnitrogen is being adsorbed, is passing through the adsorbent material.The MTZ divides the column 130 into two segments: a nitrogen-richsegment where the MTZ has passed through, and an oxygen-rich segmentahead of the moving MTZ. The MTZ forms at the inlet 132 at the start ofthe process and gradually moves through the column to the outlet 134 asthe process proceeds. Outlet end 134 of column 130 is connected to mainreservoir 158 through main valve 140, check valve 153, and productcontrol pump 154, so that oxygen-rich product gas from column 130 ispumped into reservoir 158.

In the evacuation phase, column 130 is brought to a stronger vacuum byvacuum pump 144, causing the adsorbed component, i.e. nitrogen, to bedesorbed. The nitrogen is evacuated from column 130 through main valve140, and is discharged by vacuum pump 144 as waste exhaust 177.

In the repressurization phase, the previously evacuated column 130 isreturned to near 1 atm. Ambient air 162 enters column 130 through inletend 132, and recycled product gas from product line 176 enters column130 through outlet end 134. The gases replace the vacuum that waspreviously drawn in column 130 during the evacuation phase. Just priorto column 130 reaching about 1 atm, the repressurization phase ends andthe feed phase of the cycle begins again.

This constitutes the general principles of vacuum swing adsorption (VSA)for gas separation. All phases can be accomplished with a single column,or with a plurality of columns. If a plurality of columns are used, itis preferable to have a multiple of three (illustrated as 130 a-130 c inFIG. 5) that are sequenced out of phase for the different cycle phasesin order to maintain constant product flow.

The Feed Phase—Breakthrough Detection

During the feed phase of the separation cycle, the position of the MTZwithin adsorbent column 130 is monitored, determined, and beneficiallyused to control the termination of the feed phase. The control resultsin improvements in product purity and recovery with concomitant decreasein energy consumed, as well as system size and system weight for a givenvolume of product produced.

Breakthrough is defined as the point when the MTZ reaches outlet 134 ofadsorbent column 130. At this point, feed gas begins to flow into theseparated product gas stream. This is undesirable because the purity ofthe product stream is reduced by the feed stream gas if the feed isallowed to continue past this point. Conversely, if the feed phase isterminated before the MTZ nears outlet 134 of column 130, productrecovery will be reduced because product gas contained in column 130between the MTZ and outlet 134 of column 130 will be subjected to theevacuation phase that follows the feed phase in the separation cycle,and much of this remaining product gas will be lost with the desorbedgas in the waste stream.

For a particular column geometry, temperature, adsorbent type andcondition, and cycle vacuum levels, there is an optimal time during thefeed phase of the cycle to terminate the feed—before purity requirementsare compromised, but after the maximum possible product has beenrecovered from column 130. This optimal time is determined by thedetection of the passage of the mass transfer zone through a specificposition relative to outlet end 134 of column 130.

For some combinations of system variables, the optimum feed terminationtime corresponds to the beginning of breakthrough when the leading edgeof the MTZ has just reached outlet end 134 of column 130. This event canbe detected by monitoring either or both of the gas flow rates at inlet132 or outlet 134 to column 130. Before breakthrough, the outlet flowrate is less than the inlet flow rate by an amount equal to the rate ofnitrogen gas adsorption of column 130 from the feed gas flow. Afterbreakthrough, column 130 is no longer adsorbing nitrogen from the feedgas, so the inflow and outflow rates of column 130 become equal. Anymethod of measuring gas flow rates to determine the point in time whenthese flow rates begin the transition toward equality can be used todetect this beginning of breakthrough.

It has been determined that if the inflow rate of air to column 130 ismaintained constant, a simple detection of a significant rise in slopeof the outflow rate marks breakthrough. Conversely, if the outflow rateis held fairly steady, then a falling slope of the inflow rate marks thebreakthrough. Monitoring the ratio of flow for the inlet and outlet anddetecting a significant change in the ratio of flows toward a ratio of1:1 can mark breakthrough in systems where inflow or outflow may not besteady enough to detect breakthrough by monitoring just one of the flowrates.

For other combinations of system variables, the optimum feed terminationtime may correspond to the MTZ position prior to breakthrough. In thesecases, it is beneficial for a specific amount of product to beintentionally left in column 130 at the end of a feed phase. Detectingthe position of the MTZ before breakthrough can be accomplished byadditional methods.

One method used determines the volume of gas passed into or out ofadsorbent column 130 up to the point of breakthrough by integrating theflow rate during the time interval between an initial feed andbreakthrough while using some breakthrough detection method aspreviously described. Volume of flow may also be directly measured byphysical equivalent methods using displacements of known volumes. Oncethe volume of gas that passes the column up to the point of breakthroughis determined, the volume of gas flow can be monitored during subsequentfeed phases and the feed terminated when the volume reaches a specificvalue less than that for breakthrough. At any time during the feedphase, the volume of gas passed through column 130 since the beginningof feed divided by the volume of gas at breakthrough will be the sameratio as the position of the mass transfer zone divided by the length ofcolumn 130 (assuming a constant cross sectional area along the length).Using this relationship, the position of the MTZ within column 130 canbe adequately determined during the feed phase.

The components of oxygen concentrator 100 as previously described areused to complete the cyclical phases of VSA to separate gases. The feedphase operates at a slight vacuum just below ambient (in the range of0.9 to 1 atm). This provides just enough driving force to pull ambientair 162 into adsorbent column 130 through inlet filter 136. The vacuumis caused byproduct control pump 154, which is driven by the vacuumdrawn by vacuum pump 144. Product control pump 154 is a piston pump orsimilar structure that meters a volume of gas. Product control pump 154connects with a volume much greater than the piston displacement volume,such as main reservoir 158.

The feed phase is allowed to proceed until breakthrough is detected. Upto this point, the outflow gas from adsorbent column 130 has been a highpurity oxygen/argon, low percent nitrogen mixture. The MTZ position iscontrolled to minimize nitrogen into the product gas mixture. The MTZposition is monitored by breakthrough flow sensor 150, which detects alarge increase in flow rate associated with breakthrough when thenitrogen no longer is preferentially adsorbed by adsorbent column 130.Breakthrough flow sensor is located near the column inlet 132, columnoutlet 134, or similar place where the flow rate being measured isaccessible. When the increase MTZ flow is detected, a signal is sent toECM 148, which also receives valve position signal 180 from the valveposition sensor 152. The ECM 148 compares the timing of the MTZbreakthrough signal and the valve position signal and makes a minoradjustment to motor speed 200 based on lead, lag, or on-time status tokeep the breakthrough time near the end of each feed phase. Alternately,ECM 148 receives a signal from breakthrough flow sensor 150 andimmediately terminates the current feed phase in column 130 by signalingvalve 140.to rotate to start the next phase. In yet another embodiment,the separation system contains a shut off valve that is signaled toclose the feed of ambient air 162 into column 130, or the delivery ofproduct gas from the column upon breakthrough detection.

In another embodiment, the method for determining the position of themass transfer zone prior to breakthrough is accomplished by placing asmall amount of non-adsorbing material within adsorbent column 130 at aparticular position. When the mass transfer zone passes through thisposition, a flow change is detectable as the adsorption of gas isbriefly interrupted by the non-adsorbing segment of column 130. Theresulting flow change is detectable using the same methods forbreakthrough detection previously described.

With larger columns and slower feed phases, the position of the masstransfer zone has been established by measuring temperature rise atpositions of interest within column 130. Significant temperatureincreases result from the heat of adsorption at the MTZ and can bedetected by thermistors or similar devices placed within column 130.

The Evacuation Phase

The evacuation phase brings the gas in adsorbent column 130 that wasjust in the feed phase to a vacuum state. At the end of the feed phase,the adsorbent column 130 is in equilibrium with the air infeed mixturenear 1 atm from column inlet 132 up to the MTZ. Hence, if the endingposition of the MTZ is established, and the nitrogen, oxygen, and argonisotherms for the chosen adsorbent mass are known, then the quantity ofthese gases present in adsorbent column 130 at the end of each feedphase is known. Vacuum pump 144 draws a vacuum on adsorbent column 130.This vacuum level is determined and set to a state that will remove alarge portion of the gas left in column 130. In one embodiment, this is0.2 to 0.3 atm. By percentage, the vast majority of gas discharged isnitrogen. The evacuated gas is discharged as waste from exhaust 177 ofvacuum pump 144. The preferred embodiment uses a fixed displacement typeof vacuum pump 144. During each evacuation phase, the adsorbed gas incolumn 130 is expanded into a much larger volume made up of the columnvolume plus the fixed displacement volume of pump 144.

The evacuate phase creates a self regulating effect that compensates forreductions in the amount of nitrogen adsorbed by adsorbent column 130 asthe adsorbent degrades (ages). If the adsorbent loses efficiency, lessnitrogen will be present in column 130 at the end of the phase, but thevolume of the pump that the nitrogen expands into remains the same. Astronger vacuum will result that will remove more nitrogen and thereforeallow more air to be fed during the next feed phase. A more constantbreakthrough time results and provides a more robust product cycle.

The evacuation is provided by vacuum pump 144, which is controlled andactivated by drive 146. The volume removed for each cycle of the vacuumpump 144 will remain constant, but the motor drive output 200 will becontrolled by the rate of product gas used by patient P. The amount ofoxygen used by patient P depends on the patient P's on-demandrespiratory rate, which is sensed by the device and from a variableposition switch which sends an input 192 from user interface 114 to ECM148, which in turn provides motor drive output 200 to drive 146. Thisdetermines the speed of each successive phase and, therefore, the oxygenproduction rate.

In one embodiment, a purge is applied at the very end of an evacuationphase. While still in the evacuation phase, a purge of product gas(mostly oxygen) introduced through outlet 134 effectively drives out aportion of nitrogen in column 130 through inlet 132. Adding the purgegas of high purity oxygen/argon through outlet 134 desorbs more nitrogenfrom outlet 134 of column 130, and pushes the nitrogen toward inlet 132of adsorbent column 130 and creates an ordering of the gases. The purgevolume is a function of vacuum level and adsorbent characteristics. Apurge portion of the evacuation phase is not a necessary phase for afunctioning device, but allows high oxygen purity to be maintained withweaker vacuum levels.

The Repressurization Phase

The repressurization phase brings adsorbent column 130 (just previouslyevacuated and purged) up to the feed pressure. In one embodiment, thegas used for repressurization is from both the infeed ambient air 162and a counter stream from the (oxygen-rich) product gas line 176 fromthe main reservoir 158. Alternately, the repressurization of product gascan be accomplished through valve design negating the need for aseparate line. The product gas is dispensed from a stream of product gasfrom the adsorbent column that is in the feed phase through a vacuumbreak valve used during repressurization. Repressurization with productgas can be done before, simultaneously, or after partial pressurizationwith ambient air. Repressurization with product gas is done at theopposite end of column 130 as repressurization with ambient air 162.

The effect of adding the repressurization gas of high purityoxygen/argon through outlet 134 creates a cleaning zone at outlet 134 ofadsorbent column 130 where, during the feed phase that follows next, anystray nitrogen can be preferentially adsorbed and not discharged asproduct gas. This improves the ordering of gases in the adsorbent column130. By repeating this phase during successive cycles, the purity willcontinue to increase in the product output. Weaker vacuums require moreoxygen volume returned to column 130 during repressurization if highpurity is desired. That is, a stronger vacuum must be drawn on thecolumn 130 to effectuate the same purity of oxygen absent the use ofoxygen-rich gas as aback flush for repressurization at the outlet 134 ofcolumn 130. At the end of repressurization, the feed phase will proceed.

Valve 140 Timing (FIG. 6)

The VSA cycle comprises three phases: evacuation, repressurization, andfeed, which occur sequentially in each column 130 a-130 c. For clarity,only column 130 a will be discussed, although each phase is performed(at different times during a complete cycle) in each of columns 130a-130 c.

Starting with the evacuation phase of the cycle, a small amount ofoxygen (not illustrated) may flow into outlet 134 a of adsorption column130 a to purge adsorption column 130 a, while vacuum pump 144 withdrawsgas present at inlet 134 a of the column, i.e. nitrogen-rich gas.

During the repressurization phase, an amount of previously separatedoxygen flows into outlet 134 a of adsorption column 130 a for a shorttime, and then air is allowed to enter inlet 132 a of column 130 a thathas been previously evacuated. There may be a slight overlap of theoxygen flow into outlet 134 a of adsorption column 130 a and the airflow in the opposite direction into inlet 132 a. Air freely flows intoinlet 132 a of adsorption column 130 a upon opening of valve 140 asadsorption column 130 a has been previously evacuated during theevacuation phase.

During the feed phase, air continues to flow into inlet 132 a ofadsorption column 130 a while oxygen is removed from outlet 134 a ofcolumn 130 a by a pressure differential created by product control pump154. As the MTZ passes through the adsorption column and reaches aposition at or near outlet 134 a, vacuum pump 144 will again begin toevacuate adsorbent column 130 a and restart with the evacuation phase.In the embodiment illustrated in FIG. 6, these phases are controlled bymain valve 140.

FIG. 6 is a diagram showing timing for main valve 140, which is a rotaryvalve that moves 360° (one full revolution about a central axis) foreach complete cycle of the VSA process. In the embodiment with threecolumns 130 a-130 c, the timing for each phase of the cycle is 120°.Each column 130 a-130 c is present in a different phase for each 120° ofrotation of valve 140 that is different from the other two columns toobtain a sequence that creates a steady flow of oxygen as valve 140keeps rotating.

As shown in the timing diagram, adsorption column 130 a is in the feedphase of the cycle at a start point of zero degrees. Air is being let inthrough inlet filter 136 and column inlet 132 a while separated gasconsisting of highly concentrated oxygen is being removed through columnoutlet 134 a. A portion of the oxygen-rich product gas is used in therepressurization of column 130 b. Adsorption column 130 b is in therepressurization phase at a point of rotary valve 140 being in initialposition zero degrees. As valve 140 is turned, column outlet 134 b isfed with the oxygen-rich gas for a portion of the valve's rotation,preferably less than 120°. After the flow of oxygen-rich gas enterscolumn 130 b through the column outlet 134 b, air repressurizationthrough the opening of column inlet 132 b begins. In the embodimentshown, this takes place at a point after valve 140 has begun itsrotation and ends before it reaches a third of its rotation, or a 120°rotation.

While column 130 a is in feed phase and column 130 b is in therepressurization phase, column 130 c is in the evacuation phase. Duringthe evacuation phase, a vacuum is drawn to remove adsorbed gas throughinlet 132 c, thereby regenerating it for the following feed phase.

In the embodiment shown, each column 130 a, 130 b, and 130 c, is in adifferent phase of the cycle as one moves vertically down the diagram inFIG. 6. During the first one hundred twenty degrees of rotation of therotary valve, column 130 a is in the feed phase. Simultaneously, fromzero to one hundred twenty degrees of rotation, column 130 b is beingrepressurized, while column 130 c is being evacuated.

For the next one hundred twenty degrees of rotation of valve 140 (i.e.,from 120° to 240°), adsorption column 130 a is in the evacuation phase.At this same time, column 130 b is in the feed phase, and column 130 cis in the repressurization phase.

Moving horizontally across the diagram for column 130 a, during thefinal one hundred twenty degrees of rotation of valve 140 (i.e., from240° to 360°), column 130 a is repressurized first using separated gas,and then ambient air. Separated gas and ambient air are introduced tothe column 130 a through column inlet 132 a and column outlet 174 a atopposite ends of column 130 a. During the final one hundred twentydegrees of rotation (i.e. from 240° to 360°) of main valve 140, column130 b is in the evacuation phase, and column 130 c is in the feed phase.Upon reaching three hundred sixty degrees, valve 140 is back at itsstarting position (zero degrees), and the cycles for each column 130a-130 c restart from the zero degree position.

Oxygen Concentrator 100 Physical Components (FIGS. 7-16)

FIG. 7 shows an exploded view of the oxygen concentrator 100, whichincludes belt 104, power module 106 containing removable power pack 108,reservoir module 110, control module 112, and separation cartridgemodule 116 containing adsorbent cartridge 206. Power pack 108 has beenremoved from receptacle 210 of power module 106. Adsorbent cartridge 206has been removed from receptacle 208 of cartridge module 116. Adsorbentcartridge 206 and power pack 108 are easily removable to facilitatereplacement.

In this embodiment, power pack 108 is a rechargeable battery. Receptacle210 contains electrical contacts (not illustrated) for connection topower pack 108. Cartridge 206 contains a quick-connect attachment (notillustrated) for inlet lines 164 a-164 c, outlet lines 166 a-166 c,inlet airline 168, and final product gas line 205 (not illustrated)within receptacle 208. Also present on cartridge 206 are air inlet ports135 which receive ambient air 162 for separation. Adsorbent cartridge206 contains adsorbent material that deteriorates in efficiency as it isused and ages.

FIG. 8 is a perspective view of oxygen concentrator 100. A portion ofbelt 104 has been removed revealing back interior surface 211 and innerconnections amongst the modules, including utility tubes 212, tubepathways 214, module apertures 216 a-216 d, and module sockets 218 a-218d.

Utility tubes 212 run between the adjacent modules and contain eitherelectrical wiring or pneumatic lines, or comprise pneumatic lines andelectrical wiring and associated connections. Tubes 212 are constructedto be flexible and bend as belt 104 is manipulated. If the tubes 212contain electrical lines, the tubes are constructed from a dielectricmaterial to insulate electrical wires, or similar material commonly usedin electrical connections. If the tubes 212 comprise pneumatic lines,they may be air tight, small diameter polyvinyl or PVC tubes to connectthe various gas input, gas separation, and gas removal systems of theoxygen concentrator 100. Tubes 212 contain openings or connections asrequired for electrical and pneumatic communication with each module.The back interior surface 211 of belt 104 contains tube pathways 214.Pathways 214 fabricated on the interior surface 211 of belt 104 allowthe utility tubes 212 to extend between the modules 106, 110, 112, and116. Tube pathways 214 create a semi-partitioned area on back interiorsurface 211 of belt 104 which support tubes 212.

Belt 104 is fabricated to contain apertures 216 a-216 d which allowmodules 106, 110, 112, and 116 to connect utility tubes 212 of belt 104through sockets 218 a-218 d. Apertures 216 a-216 d and sockets 218 a-218d are fabricated as part of modules 106, 110, 112, and 116. Serrations118 can be seen between the upper and lower edges 220 and 222 of belt104. When fabrication of belt 104 is completed, padding will be insertedbetween edges 220 and 222, and material will be wrapped around creatingserrations 118 and belt segments 120 to complete belt 104 as illustratedin FIG. 3. The padding is fabricated over the top of tubes 212 and tubepathways 214, or separately fabricated and fastened to back interiorsurface 211 during assembly of belt 104. Individual modules allow thedevice to flex when mounted about a curved surface, such as a beltaround patient P's waist. The construction of belt 104 with tubes 212allows patient P to manipulate the oxygen concentrator 100, such as bybending belt 104 to wear around the waist, place on docking station 122,or folding concentrator 100 in half for transport in a carryall.

FIG. 9 is a perspective view of modules 106, 110, 112, and 116 of oxygenconcentrator 100. In this view, belt 104 has been removed to illustratethe positions of sockets 218 a-218 d containing apertures 216 a-216 d oneach respective module 106, 110, 112, and 116. Each respective module106, 110, 112, and 116 is constructed from a thermoplastic material suchas acrylanitrile butadine styrene (ABS) or high density polyethylene(HDPE), or a lightweight metal or a similar rigid material that isoxidation resistant.

Each module 106, 110, 112, and 116, comprises a case portion 224, 226,228, and 230, defining the outer volume of each respectively. Bottompadding 232, 234, 236, and 238, covers the lower base portion of eachmodule 106, 110, 112, and 116, respectively. Similarly, top padding 240extends around the top perimeter of power module 106, while top padding242 and 244 covers the top portions of modules 110 and 112. Power packtop padding 246 covers the top portion of power pack 108 and cartridgetop padding 248 covers the top of separation cartridge 206. Padding222-248 is a foam or similar lightweight material that adds protectionto the modules as well as acts to reduce vibration of oxygenconcentrator 100 felt by patient P. Alternately, oxygen concentrator 100is enclosed in soft, flexible material to further increase comfort andmaintain flexibility. In one embodiment, padding 232-248 is fabricatedseparately from the modules 106, 110, 112, and 116, power pack 108 andcartridge 206. In assembling the oxygen concentrator 100, padding232-248 and case portions 224, 226, 228, and 230, are merged and securedeither using fasteners, adhesives, or a manufacturing process such asultrasonic welding.

Case portions 224, 226, 228, and 230, of each of the modules 106, 110,112, and 116, contain sockets 218 a-218 d fabricated on the surface thatcontacts belt 104. Socket 218 a-218 d for each module is constructed tohave support paths 250 for electrical wiring and pneumatic tubingsimilar to those contained within belt 104 represented by tube pathways214. Sockets 218 a-218 d are constructed so that support paths 250 onsockets 218 a-218 d align with tube pathways 214 in belt 104 when eachindividual module 106, 110, 112, and 116, is connected to belt 104. Inone embodiment, sockets 218 a-218 d are constructed to allow eachindividual module 106, 110, 112, and 116, to snap onto belt 104 orattach in a similar quick connect fashion. Utility tubes 212 comprisequick connects at module apertures 216 a-216 d. Apertures 216 a-216 dare openings in the case portions 224, 226, 228, and 230, provided forconnection of utility tubes 212 to components contained within eachmodule 106, 110, 112, and 116. This allows for removal of a singlemodule 106, 110, 112, or 116 should a specific component requiremaintenance or replacement. Sockets 218 a-218 d are constructed from thesame material as the case portions 224, 226, 228, and 230.

FIG. 10 is a perspective view of the components contained within modules106, 110, 112, and 116, and the associated pneumatic and electricalconnections of oxygen concentrator 100. Illustrated are power pack 108,valve 140, drive reducer 142, vacuum pump 144, drive 146, oxygenaccumulator 252 (comprising product control pump 154, check valves 153and 156, and reservoir 158), dispensing valve 160 connected to nasalpressure sensor line 190 and dispensing valve open line 198, columninlet lines 164 a-164 c, column outlet lines 166 a-166 c, productcontrol pump vacuum line 172, product control pump inlet line 174,product gas line 202, final product gas line 205, adsorbent cartridge206, and main electrical cable 254.

Main electrical cable 254 contains a set of electrical wires that carryinputs 178, 180, 182, 188, and 190, outputs 192 and 198, and power lines186, 198, and 200 shown in FIG. 5. Main electrical cable 254 extendsfrom power pack 108 to ECM 148 (not visible in FIG. 10). Dispensingvalve time open output 198 and nasal pressure sensor input 190 are wiresthat extend between ECM 148 and dispensing valve 160. Similarly, theother inputs and outputs are wired to the appropriate system componentsas illustrated in FIG. 5 (although not specifically illustrated in FIG.10.)

Product gas line 202 connects dispensing valve 160 with reservoir 158 ofaccumulator 252. Final product gas line 205 connects dispensing valve160 to product gas outlet port 103 for connection to delivery tube 102after passing through final filter 136 located in adsorbent cartridge206 to provide patient P with oxygen rich product gas. Product controlpump inlet line 174 extends from main valve 140 to product control pump154, which pumps separated oxygen rich gas into reservoir 158. Vacuumline 172 connects product control pump 154 through valve 140 to a vacuumdrawn by vacuum pump 144, and provides the actuation for product controlpump 154. Column inlet lines 164 a-164 c and column outlet lines 166a-166 c connect main valve 140 with column inlet ports 132 a-132 c andcolumn outlet ports 134 a-134 c of columns 130 a-130 c, respectively(not illustrated). Inlet air line 168 transports ambient air 162 fromseparation cartridge 206 to main valve 140, while vacuum inlet line 170connects vacuum pump 144 to main valve 140. All lines 164 a-164 c, 166a-166 c, 168, 170, 172, 174, 176, 202, and 205, are pneumatic lines orsimilar structures that allow for the isolated flow of gases betweensystem components.

FIG. 11 is a perspective view of the components contained within powermodule 106: power pack 108 (comprising cells 256, outer wall 258, andpower pack life indicator 260) and dispensing valve 160. In theembodiment illustrated, power pack 108 is a lithium-ion battery packcomprised of five cells 256. Individual cells 256 are contained withinouter wall 258, part of which has been removed to show cell 256. Powerpack 108 is a battery that is rechargeable and removable from powermodule 106. Although illustrated as a trapezoid containing fivecylindrical cells, the shape and number of cells will vary depending onthe shape of power module 106 and power requirements of oxygenconcentrator 100.

Power pack 108 is a lithium based battery pack capable of beingrecharged in a recharging socket or station that connects to an externalpower supply. Alternatively, power pack 108 comprises a battery or fuelcell. In one embodiment, power pack 108 is a lithium ion battery packthat is constructed from several interconnected lithium-ion batteries.Oxygen concentrator 100 uses a maximum of fifteen watts of power. Thisresults in a battery weight of less than 0.7 pounds (0.3 kg). In thisembodiment, patient P taking twenty breaths per minute at a setting of 2liters per minute equivalent can use oxygen concentrator 100 for aminimum of four hours on a fully charged battery. Power pack 108 iseasily exchanged with another similar battery pack, and can be removedwith a simple pulling or tugging motion. In another embodiment (notillustrated), oxygen concentrator 100 contains a jack for receiving apower cord which can then be plugged into either a 110 volt wall outletor a 12 volt power supply system (such as a car utility plug) so thatpower pack 108 can be charged in place in oxygen concentrator 100.

Power pack life indicator 260 displays the amount of time left that thepower pack will operate the oxygen concentrator 100. As illustrated,power pack life indicator 260 is a display, such as a liquid-crystaldisplay (LCD) or light emitting diode (LED) screen, with numeric outputof expected life in hours. The LCD or LED screen may also contain aseries of bars that act as indicators. Alternately, power pack lifeindicator 260 is a light or series of lights.

Dispensing valve 160 is contained within power module 106 and is used tofeed the flow of oxygen to patient P. Dispensing valve 160 is a valveactivated by a change in pressure, such as that caused when a person isinhaling. A sensor in the dispensing valve circuit monitors pressure,and opens dispensing valve 160 when a drop in pressure is sensed. ECM148 communicates with dispensing valve 160 through input 190 and output198 (see FIG. 5). Dispensing valve 160 is in communication withreservoir 158 through product gas line 202. Reservoir 158 is kept at aslight pressure above ambient. Thus, when dispensing valve 160 isopened, oxygen rich gas will flow from reservoir 158 through finalproduct gas line 205, final product filter 138, and product gas outletport 103 for delivery to patient P through tubing 102. The flow of gasis further assisted by the pressure drop created by patient P'sinhaling. Dispensing valve 160 can be set to deliver oxygen rich gas topatient P for the beginning portion of a breath when patient P firstinhales rather than the whole breath.

Dispensing valve 160 provides for operating oxygen concentrator 100 inone of two possible modes: pulse flow or continuous flow. When patient Pis using the oxygen concentrator 100 in the pulse flow mode, dispensingvalve 160 will open intermittently in response to inhalation and willstay open for a pulse time according to the setting of the controls asset by patient P. If continuous flow is desired, dispensing valve 160 ismaintained at an open or partially opened state. The product isdispensed to patient P though oxygen delivery tube 102 at a continuousrate, typically in the range of 1-1.5 lpm (liters per minute). Thepressure difference corresponding to a dispensing orifice in deliverytube 102 will accommodate the flow rate from the reservoir 158.

FIGS. 12 a-12 d are various views of components contained inside ofreservoir module 110. FIG. 12 a is a perspective view of accumulator252. FIG. 12 b is a top view of accumulator 12 b. FIGS. 12 c and 12 dare sectional views corresponding to the section lines in 12 b.Contained within reservoir module 110 is oxygen accumulator 252(comprising reservoir 158, check valves 153 and 156, and product controlpump 154), inlet port 261, and outlet port 263. Accumulator 252 receivesseparated product gas through inlet port 261. Product inlet line 174(shown in FIG. 10) is connected to inlet port 261 and links productcontrol pump 154 to separation cartridge 206 through main valve 140 totransport oxygen rich gas separated by cartridge 206. Inlet port 261connects to check valve 153 which allows product gas into productcontrol pump 154.

Product control pump 154 includes piston 262, actuated by spring 264within pump chamber 265, which pushes separated oxygen-rich product gasinto reservoir 158. Check valve 156 opens to allow oxygen into thereservoir 158 and closes to prevent back flow of oxygen-rich gas whenthe desired pressure in reservoir 158 is attained. The low pressure ofreservoir 158 exerts a force on check valve 156 to keep valve 156closed. Reservoir 158 takes oxygen-rich gas produced by oxygenconcentrator 100 and stores it at a low pressure above ambient until theproduct is required for use by patient P.

Product control pump 154 is driven by vacuum. Product control pumpvacuum line 174 is connected to the vacuum drawn by vacuum pump 144through main valve 140. When a vacuum is drawn, the force draws piston262 down to compress spring 264 which expands pump chamber 265, andcauses check valve 153 to open. Oxygen-rich gas from separationcartridge 206 flows through check valve 153 and enters pump chamber 265in the volume created by the displacement of piston 262. At theappropriate time in the cycle, valve 140 will interrupt the vacuum toproduct control pump 154, and spring 264 will force piston 262 upwards.The movement of piston 262 will force oxygen rich gas in pump chamber265 through check valve 156 and into reservoir 158. At the same time,check valve 153 closes to prevent more gas from entering pump 154. Withthis embodiment, no additional drive (other than the vacuum to pullpiston 262 down and the spring force to move it up) is required forproduct control pump 154 which adds to the overall efficiency of thesystem.

In one embodiment, reservoir 158 has a capacity that is about four timeslarger than the size of the largest pulse provided by oxygenconcentrator 100. In one embodiment, extra volume is included to accountfor separated oxygen used as a back flow in adsorbent columns 130 a-130c. Specifically, main storage reservoir 158 for oxygen concentrator 100can be designed according to the flow rates listed in Table 1. Storagereservoir 158 is 100 cc (cubic centimeters) to 400 cc in volume. Mainstorage reservoir 158 is maintained at a low pressure to providedelivery of the product gas to patient P through outlet 263 which isconnected to final product dispensing line 202. In one embodiment, thepressure is between 1 atm (ambient) and 1.5 atm. Also acceptable arepressures less than eight psi (55,158 Pa), with a pressure of two andone half to five psi (17,236 to 34,473 Pa) preferred. The low pressureof reservoir 158 allows oxygen concentrator 100 to be used in most areaswhere high pressure oxygen is banned. Also, low pressure requires lessenergy to fill reservoir 158, which adds to the efficiency of the systemby requiring a simpler pressurizing mechanism compared to high pressuresystems.

Reservoir 158 contains pressure sensor 159 (such as a piezoresistive orcapacitive sensor) that sends reservoir pressure signal 188 to ECM 148(see FIG. 5). ECM 148 adjusts the speed of the motor of drive 146 basedon reservoir pressure signal 188 in combination with the currentsettings on user interface 114. As patient P's respiratory rateincreases for the current setting, more oxygen-rich gas from reservoir158 is dispensed thus lowering the pressure of reservoir 158. The dropin pressure is sensed and the system will react by increasing theproduction of product gas. Similarly, a decrease in the respiratory rateof patient P at the current setting of oxygen concentrator 100 raisesthe pressure in reservoir 158. The rise in pressure is sensed and ECM148 adjusts drive 146 accordingly to maintain a preset pressure range inreservoir 158. Thus, only the amount of oxygen used by patient P isproduced by oxygen concentrator 100.

FIG. 13 is a perspective view of the control module 112. Illustrated arethe case 228 containing aperture 216 c and socket 218 c, and padding 236and 234. Control module 112 contains user interface 114 comprising powerswitch 266, flow level indicator lights 268, flow setting switches 270 aand 270 b, boost switch 272, and indicator lights 274 and 276. Powerswitch 266 is an ordinary toggle or push button switch capable ofturning oxygen concentrator 100 on and off.

Flow settings are dually controlled by patient P utilizing flow settingswitches 270. First, continuous or pulse mode is selected by patient P.In a continuous flow mode, oxygen is dispensed at a continuous flow ratesuch as one to one and a half liters per minute. If oxygen concentrator100 is set in a pulse mode for controlling flow, oxygen concentrator 100utilizes dispensing valve 160 to provide pulse dispensing of productgas. The pulse mode is set to meet patient P's needs for the equivalentof one to five liters per minute of continuous oxygen flow. In oneembodiment, a dial containing settings of one to five is utilized. Inthe embodiment illustrated in FIG. 13, flow setting switches are used toadjust the flow rate between various stepped levels. Each settingcorresponds to the specific value for continuous flow, or acorresponding pulse volume. For example, settings for a pulse mode arecontained in the table below. TABLE 1 Total Volume Trigger Pulse FlowPulse Peak Pulse Set- Pulse Range Time Ramp Rate Duration Flow ting(cc/pulse) (sec) (sec) Max (sec) (LPM) 1 10 to 12 .001 to .02 .03 to .07.15 14 2 20 to 24 .001 to .02 .03 to .07 .20 14 3 30 to 36 .001 to .02.03 to .07 .25 15 4 40 to 48 .001 to .02 .03 to .07 .30 16 5 50 to 60.001 to .02 .03 to .07 .35 17

When the unit is set in pulse mode, product gas is dispensed only at thebeginning of inhalation. In one embodiment, product dispensing valve 160is only opened between zero and 0.4 seconds of the beginning of a breathof patient P. This controls the amount of oxygen removed from reservoir158. In another embodiment, oxygen concentrator 100 is shut off if nopressure drop is sensed by nasal pressure sensor 190 for a set amount oftime, such as two minutes, which in turn closes dispensing valve 160.

Patient P can temporarily increase (or “boost”) the flow rate of oxygenby actuating boost control switch 272 on user interface 114. When boostswitch 272 is activated, oxygen concentrator 100 increases the flow rateof oxygen for a set period of time, such as 10 minutes. After timingout, oxygen concentrator 100 returns to the previous setting. The boostfunction will not work if oxygen concentrator 100 is already operatingat the maximum flow rate.

Indicator light 274 indicates power pack 108 is running low. Indicatorlight 276 indicates that there is a problem with separation cartridge206, such as a bad connection with receptacle 208. In one embodiment,oxygen concentrator 100 contains three different colored lights: red,yellow, and green. The green light indicates that there are no problemsdetected with oxygen concentrator 100. A yellow flashing light or ayellow non-flashing light indicates a condition has been sensed thatshould be addressed. An example of such a condition is a low battery. Ared flashing light indicates that a condition has been detected thatrequires an immediate response. A red non-flashing light indicates thatoxygen concentrator 100 has failed, and has shut down. For example, ifoxygen concentrator 100 fails to produce a stream of separated gas ofeighty-five percent oxygen, oxygen concentrator 100 will detect thisproblem via breakthrough flow sensor 150. ECM 148 shuts off main valve140 so no ambient air 162 is being submitted to the gas separationcartridge 206. Product gas is no longer being supplied to reservoir 158.After a few breaths, reservoir 158 will empty, triggering reservoirpressure sensor output 188 (shown in FIG. 5), which communicates to ECM148 to shut down oxygen concentrator 100, and display the red warninglight. This signals patient P that maintenance is needed. In addition tothe aforementioned indicator lights, the unit may also contain a boostindicator light to indicate when a boost function is in operation.Similarly, an audible alarm may be included in oxygen concentrator 100to indicate failure.

FIG. 14 is a front view of the interior components of control module112. Illustrated are drive 146, vacuum pump 144, drive speed reducer142, and valve 140. Drive 146 includes a DC motor, driven by batterypower pack 108, which supplies the necessary power to operate vacuumpump 144. The motor draws a maximum of 15 watts of power. Vacuum pump144 is a positive displacement pump. In this embodiment, drive 146 runsboth vacuum pump 144 and valve 140. Vacuum pump 144 is run by the motorat one speed, while valve 140 is run off the same motor but at a reducedspeed. The reduction in speed is accomplished with gears that comprisedrive speed reducer 142 between the motor of drive 146 and valve 140.

Valve 140 is a valve containing a minimum number of ports equal to twotimes the number of adsorbent beds (columns) in separation cartridge206. Additionally, main valve 140 contains other ports for the inlet ofambient air 162, vacuum provided by vacuum pump 144, and recycling ofproduct gas used to purge columns 130 a-130 c during repressurization.In the preferred embodiment, valve 140 is a rotary valve, but may alsobe a solenoid valve, directional control valve, or series of individualvalves in communication with each other and each connected to anadsorbent column 130 a-130 c.

In an alternate embodiment, drive 146 may contain an independent motorfor operating valve 140. If valve 140 is run by an independent motor,that motor is powered by power pack 108 and synchronized with the othermotor(s) of drive 146 by ECM 148. As illustrated, drive 146 contains asingle motor and valve 140 is connected to a system of gears thatcomprise drive speed reducer 142. Alternately, drive speed reducer 142can be any common power transmission components such as pulley andbelts, or gears and sprockets.

FIG. 15 is a perspective view of separation cartridge 206 containedwithin separation cartridge module 116. Illustrated are inlet ports 132a-132 c, outlet ports 134 a-134 c, and casing 230. In the embodimentillustrated, three adsorption columns are contained within casing 230with one inlet port 132 a-132 c, and one outlet port 134 a-134 c, foreach adsorption column 130 a-130 c. Each adsorption column 130 a-130 cis a hermetically sealed container containing a bed of adsorptionmaterial, preferably a zeolite capable of adsorbing nitrogen gas, suchas lithium low silica 13× zeolite. Each bed contains between five andtwenty-five cubic centimeters of material, and in one embodimentcontains fifteen (plus or minus one) cubic centimeters of material. Theadsorbent bead size is a thirty by sixty mesh, wherein thirty mesh isequal to 0.0234 inches (0.0594 cm) and sixty mesh is equal to 0.01inches (0.0254 cm).

Column inlet ports 132 a-134 c are connected to receive either ambientair 162 or vacuum, while outlet ports 134 a-134 c expel product gas orreceive purge gas. This arrangement promotes ordering of gases withinthe columns 130 a-130 c by having oxygen rich gas always present at oneend of the column. This results in improved efficiency as air flowthrough the columns 130 a-130 c creates an oxygen rich zone continuouslyat one end, which allows the vacuum to evacuate and desorb thepreviously adsorbed nitrogen where it is contained in the greatestconcentration.

FIG. 16 is a perspective view of the columns 130 a-130 c and the filters136 and 138 within casing 230 of separation cartridge 206. Illustratedare final product filter 138 connected to product gas outlet port 103which connects to tubing 102, inlet air filter 136, and adsorbentcolumns 130 a-130 c each comprising spin inducers 280 a-280 f, adsorbentmaterial 282 a-282 c, porous filters 284 a-284 f, and springs 286 a-286c. Springs 286 a-286 c are coil springs that hold each adsorbent columnin compression 130 a-130 c in place within casing 230 of separationcartridge 206 to prevent movement of adsorbent beads. Spin inducers 280a-280 f help force even distribution of gases through columns 130 a-130c, which helps to keep the MTZ well defined for more accurate detection.

Adsorbent material 282 a-282 c is the same as that previously described.Filters 136 and 138 are constructed of common filtering materials andare used to remove dust and other large particulate matter from the airstreams to assure that the flow of oxygen out to patient P is free ofsuch materials. Porous filters 284 a-284 f are a small section ofmaterial commonly used as a particle filter provided at each end ofcolumns 130 a-130 c. Porous filters 284 a-284 f act to prevent adsorbentparticles from contacting the mechanisms and valving of concentrator100.

Docking Station 122 (FIGS. 17-18)

FIG. 17 is a perspective view of the back side of oxygen concentrator100 on docking station 122. Illustrated are oxygen concentrator 100comprising power module 106, reservoir module 110, control module 112,and separation cartridge module 116, belt 104, and docking station 122containing status display 288. Status display 288 is an LED, LCD, orsimilar digital display used to provide information to patient P such astime of day, time the concentrator has been used, time of recharging forpower pack 108, or similar information. Additionally, docking station122 may contain other controls (not illustrated) including a boostsetting while the concentrator is docked, a mode switch for switchingbetween pulse and continuous flow of oxygen, and indicator lights toshow expected battery life, adsorbent column life, gas input, gasoutput, or gas separation system malfunctions, or other similar itemsthat were previously described as part of user interface 114.

FIG. 18 is a perspective view of the docking station 122 with oxygenconcentrator 100 removed. Concentrator dock 126 is visible on dockingstation 122 with oxygen concentrator 100 removed. Concentrator dock 126may optionally contain electrical connections (not illustrated) tocharge power pack 108 contained within power module 106 while oxygenconcentrator 100 is docked. Additionally, docking station 122 contains apower cord (not illustrated) available to connect to a wall socket orother power source such as a car utility plug. Docking station 122 usespower provided through the power cord to operate oxygen concentrator 100and/or recharge power packs 108. Docking station 122 contains a flatbottom 290 to rest on a level surface and allow oxygen concentrator 100to be in the docking station without moving. Alternately, dockingstation 122 is mountable to a wall in one embodiment, and is a freestanding device that is set on a generally flat surface in anotherembodiment.

In one embodiment, docking station 122 comprises indicator lights andcontrol power switch (not illustrated) in addition to status display288, power pack chargers 124 a and 124 b, and concentrator dock 126.Indicator lights provide information to patient P utilizing oxygenconcentrator 100. Indicator lights will indicate if oxygen concentrator100 is functioning properly, requires maintenance, or has failed.Control switch is a master switch for supplying or terminating power orcontrolling the setting of flow for oxygen concentrator 100. Statusdisplay 128 is an LED, LCD or similar digital display that can be usedto indicate various information to patient P such as time of day, timeoxygen concentrator 100 has been docked, time of recharging for thepower pack, or similar information.

Docking station 122 also contains power pack chargers 124 a and 124 band concentrator dock 126. Docking station 122 contains a power cord(not illustrated) available to plug into a wall socket or a similarpower pack. Docking station 122 converts AC power to recharge power pack108 in power pack chargers 124 a and 124 b. Power pack chargers 124 aand 124 b contain contacts that are used to transfer power to power pack108 while recharging. Alternatively, a power pack 108 placed in charger124 a or 124 b is inductively coupled to recharge the power pack 108.Similarly, power is provided to oxygen concentrator 100 itself while ondocking station 122, and to recharge of the power pack 108 (see FIG. 4)still attached to the oxygen concentrator 100. Concentrator dock 126 isshaped to provide a place to set oxygen concentrator 100 while docked,as well as facilitate easy removal of oxygen concentrator 100 forambulatory use.

In one embodiment, docking station 122 performs several functions withoxygen concentrator 100 docked. First, oxygen concentrator 100 isallowed to run without utilizing power pack 108 while it is docked.Second, a boost setting is available to increase the delivery rate ofoxygen while oxygen concentrator 100 is docked. Boost switch 272 islocated on user interface 114 (See FIG. 13). In an alternate embodiment,a boost switch is located on docking station 122. Upon removal of oxygenconcentrator 100 from docking station 122, the boost setting is removedand oxygen concentrator 100 operates at a set delivery rate in either acontinuous or pulse mode.

Oxygen concentrator 100 contains flow setting switch 270 (FIG. 13), anda mode switch (not illustrated). The mode switch allows patient P toselect continuous or pulse flow. In one embodiment, patient P is allowedto adjust the setting of oxygen concentrator 100 only while docked. Thatis, patient P can reprogram by changing a pulse setting (e.g., from 2 to3), or continuous flow mode (e.g., from 1.0 to 1.5 liters per minute),only while oxygen concentrator 100 is on docking station 122. Patient Pwishing to adjust settings will be required to hold the control switchwhile adjusting the flow setting dial or mode switch. In anotherembodiment, docking station 122 contains a switch automaticallyactivated by placing oxygen concentrator 100 in docking station 122which allows patient P to adjust flow setting. The requirement thatsettings can only be changed during docking prevents accidentalswitching of the flow mode of oxygen concentrator 100 during ambulatoryuse. For example, there is no change in flow if flow setting switch 130is bumped, which would normally increase oxygen flow. If oxygenconcentrator 100 can only be reprogrammed in docking station 122, oxygenconcentrator 100 will remain in the preset mode set at docking station122 and will not increase or decrease flow by a change of the setting.In one embodiment, the flow setting switch and mode switch are locatedon a user interface located directly on docking station 122.

Another function of docking station 122 is to provide diagnosticfeatures of the system. Docking station 122 may indicate expectedbattery life, adsorbent column life, or pump malfunctions through theuse of indicator lights, or status display 128, or a combination ofboth. Alternatively, these items are located on user interface 114, orat a combination of locations of user interface 114 and docking station122. For example, battery life indicator 142 is located directly onpower pack 108 that comprises the battery itself, and battery problemwarning light 274 is on user interface 114 also. Similarly, adsorbentcartridge warning light 276 is located on user interface 114, but mayalso be on either the cartridge module 116 or docking station 122 aswell.

Concentrator Efficiency

Oxygen concentrator 100 can produce a stream of product gas containing arange of 85-95 percent oxygen which provides up to 5 liters per minutepulsed equivalent of product gas. By utilizing vacuum swing adsorption,the separation process phases are all performed at less than 1 atm.

Utilizing a vacuum to exhaust unwanted gas from adsorbent columns 130a-130 c improves efficiency of the oxygen concentrator 100. Less poweris required than pressure swing adsorption (PSA) or vacuum-pressureswing adsorption (VPSA), which results in a smaller battery and thus alighter weight product. Oxygen concentrator 100 as disclosed weighs lessthan 3 pounds (1.4 kg) and occupies less than 1 liter of volume. Also,the efficiency of the system allows for oxygen concentrator 100 tooperate for at least three hours while producing up to 5 liters perminute pulsed equivalent of product gas without requiring patient P toattend to the unit, e.g. changing the battery. Further, the low energyconsumption causes less heat transfer. The product gas is dischargedfrom the separation system at a temperature of ±six degrees Celsius fromthat of the ambient air. This eliminates the need for heat exchangerswhich add to the overall weight and reduces system efficiency. Theamount of heat generated causes no discomfort to patient P wearing andutilizing the oxygen concentrator 100. Also, upon starting oxygenconcentrator 100, the flow of product gas will increase from 21 percentoxygen (ambient) to 85 percent or more oxygen in under two minutes.

Improvements over the prior art are attained by regulating the device toonly separate the amount of oxygen needed by patient P at any giventime. The prior art separates a flow of oxygen and delivers that rate topatient P as a steady flow. Patient P is only inhaling this oxygenduring about ⅓ of the normal breathing cycle. Within the inhalationportion of the breathing cycle, the volume of gas inhaled last stays inthe dead space of the airways and is not presented to the alveoli.Therefore if oxygen is dispensed to patient P only during the early partof inhalation, less than ⅓ the steady flow is actually required.Moreover, prior art devices do not adjust the flow based on a patientP's needs, but operate at the same steady flow. The present concentratorslows down its entire cycle rate producing only the amount of oxygenneeded. Thus, oxygen concentrator 100 retains a high oxygen recoverypercentage at all product flow rates while minimizing energy consumptionand maximizing adsorbent life. Patient P's actual needs vary with realtime changes in activity. This causes a corresponding variation inbreathing rate. Oxygen concentrator 100 tracks patient P's breathingrate and adjusts oxygen separation and delivery rates proportionally. Incombination, these two features allow oxygen concentrator 100 toseparate oxygen only at the rate it is being consumed, resulting in areduction in the amount of oxygen needing to be separated for patient P.

Another improvement over the prior art involves reducing the waste ofseparated oxygen in the various adsorb and desorb cycle phases. This istypically referred to as maximizing product recovery. The primary systemcomponents become larger or smaller as the amount of oxygen separatedincreases or decreases. Therefore, a dramatic reduction in size andweight of the concentrator requires use of as much separated oxygen aspossible by delivering it to patient P rather than losing it to thewaste stream. The prior art works by using the Skarstrom cycle wellknown to those skilled in the art.

During one phase of the Skarstrom cycle in PSA or VPSA, air is pumpedinto one end of a column of adsorbent pressurizing it above atmosphericpressure while oxygen is flowing out of the opposing end. Nitrogen isbeing adsorbed as the MTZ propagates toward the oxygen outlet end of thecolumn. This phase is terminated before the MTZ breaks through into theoxygen stream so that oxygen purity is not diluted by the nitrogen richair trailing the MTZ. If it is terminated earlier than necessary tomaintain purity there will be substantial separated oxygen left in thecolumn in front of the MTZ that is not passed to the patient. During thenext cycle phase the column pressure is reduced to a lower cyclepressure desorbing the nitrogen that was adsorbed during the separationphase and it is passed to the waste stream. Some of the oxygen left inthe column at higher pressure will also be passed to the waste stream asgas flows from the column when pressure is reduced. Recovery ofseparated oxygen can 110 therefore be maximized by stopping the previousseparation phase just short of breakthrough, leaving minimal oxygen inthe column to be lost to the waste stream during the reduced pressureevacuation phase. The position of the MTZ needs to be accurately knownto terminate the separation phase for optimal recovery withoutcompromising purity. This position cannot be accurately estimatedbecause its propagation rate is a function of many variables includingproduct oxygen flow rate, high and low cycle pressures, temperature,adsorbent water content and the amount of other contaminants accumulatedin the adsorbent. Prior art systems stop the separation phase well shortof breakthrough to encompass worst case operating conditions withoutsacrificing purity and thereby waste separated oxygen in the evacuationphases during most typical non-worst case operating conditions.

Oxygen concentrator 100 determines the position of the MTZ just prior tobreakthrough and terminates the flow from outlet 134 for the remainderof the feed phase or adjusts the motor speed, as previously described.Additional oxygen is left in the column at the end of a feed phase andis wasted during the evacuation phases. This is oxygen adsorbed by theadsorbent combined with oxygen present in the interstitial and deadspaces of the adsorbent and column. All adsorbents used in oxygenseparators adsorb nitrogen, and also oxygen to some extent. Theadsorbent used in oxygen concentrator 100 presents a very high ratio ofadsorbed nitrogen to adsorbed oxygen. As the amount of oxygen adsorbedis minimized through the choice of an adsorbent with a low affinity foroxygen, the amount of adsorbent needed to separate a given amount ofnitrogen during a separation phase will decrease as its affinity fornitrogen increases. The less adsorbent needed to adsorb a given amountof nitrogen, the less adsorbent there is to adsorb oxygen and thesmaller the column can be with less interstitial and dead space.

For example, a LiLSX adsorbent referred to as Oxysiv MDX from UOPCorporation has a very high ratio of adsorbed nitrogen to adsorbedoxygen in the operating pressure range of oxygen concentrator 100. TheSkarstrom cycle of the prior art uses a purge phase in which separatedoxygen is fed back into the product end of the column while nitrogenrich gas is passing out of the opposing end of the column into the wastestream as the pressure transitions to the lower cycle pressure. Whilethis purge can enhance product purity, some of the purge oxygen passesall the way through the column and is lost to the waste stream. Oxygenconcentrator 100 using VSA achieves a measured 60% oxygen recovery rate,compared to a typical recovery rate of 30% for the prior art utilizingPSA.

Another improvement over the prior art concerns the choice of adsorbentand operating pressure range. The energy required by the separationprocess directly defines the weight and size of major components such asthe battery, motor and gas pump of a concentrator. Minimizing the amountof adsorbent minimizes the amount of energy needed to separate a givenamount of oxygen. Each adsorbent has a characteristic pair of isothermsthat show the amount of oxygen and nitrogen a given mass of adsorbentwill hold at equilibrium over a range of pressures and vacuums for thesegasses at a constant temperature. The cycle phases of the systemnecessarily include the pumping of gas contained in volumes of adsorbentto produce a change in nitrogen partial pressure between a chosen higherpressure and a chosen lower pressure. The pneumatic energy a pump mustdeliver in the process of cycling a given volume of gas between a higherand a lower level is in direct proportion to the volume of gas pumpedmultiplied by the difference between the high and low vacuum levels. Theisotherms for various adsorbent candidates specify the amount ofnitrogen contained in a fixed mass of adsorbent at a fixed temperatureas a function of nitrogen partial pressure.

An example of the isotherm for the LiLSX adsorbent Oxysiv MDX along withthe isotherm for a typical 13× type adsorbent used in the prior art isshown in FIG. 19. Having minimized the amount of oxygen needed to beseparated from air and having maximized the recovery percent of oxygenas previously disclosed, along with knowing the percentage of oxygenpresent in air prescribes a specific minimum amount of air that must bemoved into the system to produce the needed oxygen. This minimum amountof air minus the maximized separated oxygen must pass out of the systemas a minimized volume of waste gas. Oxygen concentrator 100 acts tominimize the flow rates of the air feed stream and the waste stream.This flow must be pumped across a pressure difference defined by thechoice of high and low operating pressures requiring a pumping energythat is proportional to both the flow rate and the pressure difference.The gas streams are pumped into or out of the adsorbent during eachcomplete cycle to produce the needed swing in pressure between high andlow cycle pressure levels allowing the separation of nitrogen fromoxygen. Minimizing the amount of gas being pumped through the systemreduces the pumping energy in proportion to reductions in the differencebetween chosen high and low pressure points that the gas must be pumpedacross. The isotherm for nitrogen shows that nitrogen is transferred inor out of the adsorbent with the smallest change in pressure where theslope of the isotherm is the steepest. Using typical PSA, a ratio ofhigh to low pressure levels in these systems needs to be 3:1 or greaterto maintain the desired oxygen purity. Lower pressure ranges, i.e.sub-atmospheric or vacuum ranges used in VSA, allow this ratio to bemaintained with less total difference between the high and low pressurelevels.

For example, prior art operates between 1 and 3 atmospheres for a 3:1ratio and a pressure difference between high and low levels of 2atmospheres. Oxygen concentrator 100 using VSA operates between 0.3atmospheres and 1 atmosphere. A ratio of about 3.3:1 is achieved with apressure difference of only 0.7 atmospheres. Operating on this range ofthe isotherm as seen in FIG. 19 allows just as much nitrogen to bepassed in and out of the LiLSX adsorbent with a 0.7 atmosphere pressurerange as a PSA system does with 13× adsorbent and a 2.0 atmospherepressure range. The LiLSX adsorbent allows a cycle pressure range thatis nearly ⅓ that of a PSA system with a proportional reduction inpumping energy.

Oxygen concentrator 100 is a quiet device. When oxygen concentrator 100is running, it produces a noise level in the range often to thirtydecibels. Further, with the compact size of the parts, vacuum pump 144is running continuously and there is very little vibration to affect aperson using it docked or wearing it as an ambulatory device. The deviceof the present invention with the described components weighs less thanthree pounds (1.36 kg). The compact size (less than about 61 cu. in.(1000 cc)) allows for easy portability. Similarly, the small size doesnot disrupt counter space or storage when used at home. The device doesgive off some heat, however the outer case is less than 6 degreesCelsius higher than ambient when oxygen concentrator 100 is running onbattery power. The device may emit more heat while it is docked andoperating on AC power to charge the power pack 108, but is still lessthan 15 degrees Celsius above ambient.

Based on the foregoing embodiments, the efficiency of the concentratorcan be determined. One measure of efficiency is the ratio of oxygenproduced to the amount of adsorbent material used to obtain the oxygen,represented by the following:Qp=Liter/min O₂ producedMadsorbent=Kg of Adsorbent Materialfor example, the disclosed embodiments include adsorbent columns 130a-130 c, with each column containing 15 cubic centimeters (cc) ofadsorbent material with a density of 0.66 gm/cc. That is:${\left( {3{columns}} \right)\left( \frac{15\quad{cc}}{column} \right)\left( \frac{0.66\quad{gm}}{cc} \right)} = {30\quad{gms}\quad{for}\quad{the}\quad{{system}.}}$The following flow rates (Qp) were obtained by the above disclosedconcentrator:Qp max=1.5 L/minQp min=0.14 L/min

This results in a range for kilograms of adsorbent material to oxygenflow rate of: $0.020 < \frac{Madsorbent}{Qp} < 0.214$

Similarly, flow rates (Qp) were determined for a system that containsthree adsorption columns, each column containing 15 cc of adsorbentmaterial. The separation completed in a range of 0.3 atm to 0.95 atm.Values were calculated for breakthrough time, work, battery life, andflow rate. The volume of gas contained in a column at the end of a feedphase was 150 cc. These constants were used to determine the followingmeasures of efficiency:

Work per evacuation cycle or pneumatic power requirements weredetermined based on the following calculations:W(work)=(volume moved)*(vacuum differences);

The vacuum differences are calculated as the vacuum pump is continuouslychanging gas out, and as vacuum progresses to end point. From this:V_(H)=Vacuum upper levelV_(L)=Vacuum lower levelVol=Volume of gas in the column at end of feed phaseW=Vol*(V _(H) −V _(L))*(1+(V _(H)/(V _(H) −V _(L)))*ln(V _(L) /V_(H))+ln(V _(H) /V _(L)))Inserting the above constants and converting to joules (multiply by100.32 to get L*atm to joules) yields:W=4.81 joules

Thus, 4.81 joules is required to evacuate the gas which desorbs duringthe evacuation phase. From experimentation, the following flow rates(LPM is liters per minute) and cycle times were recorded: Qp (flow rate)Low = .14 LPM Med = .720 LPM High = 1.5 LPM Cycle time Low = 5.6 sec.Med = 1.12 sec. High = .54 sec.Power consumption can be determined by calculating work divided by thetime of the cycle.Low flow power=4.81 joule/5.6 sec=0.85 wattsMedium Flow power=4.81 joule/1.12 sec=4.29 wattsHigh flow power=4.81 joule/0.54 sec=8.9 wattsFrom the above, a measure of energy consumed to the flow rate can bemade and used as an indicator of the system efficiency:${{Low}\text{:}\frac{{.85}\quad w}{{.14}\quad{LPM}}} = {6.07\quad w\text{/}{LPM}}$${{Medium}\text{:}\frac{4.29\quad w}{{.72}{LPM}}} = {5.95\quad w\text{/}{LPM}}$${{High}\text{:}\frac{8.9\quad w}{1.5{LPM}}} = {5.93\quad w\text{/}{LPM}}$

Another measure of efficiency is the ratio of mass of the power pack(Mpowerpack) compared to the amount of oxygen produced (Qp) over time:$\frac{Mpowerpack}{{QpT}({time})}$The following constants are used in the calculation: the battery cell isa type 18650 lithium ion battery with 7.4 watts-hrs, measuring 42 g;motor efficiency is 90 percent; and vacuum pump efficiency is 80percent.${{{Pneumatic}\quad{work}} = {6\quad W\text{/}L\text{/}{\min.\quad{Thus}}}},{{{Electric}\quad{power}} = {\frac{6\quad W\text{/}{LPM}}{({.9})({.8})} = {8.3\quad W\text{/}{LPM}}}}$Battery mass compared to energy consumption is:${\frac{42\quad g}{7.4({watt})({hr})}\left( \frac{1\quad{Kg}}{1000\quad g} \right)\frac{8.3\quad{watt}}{LPM}} = {{.047}\frac{Kg}{{LPM}({HR})}}$Total battery mass for the power pack can be determined from thisequation. For example, if a patient requires the concentrator to run forfour hours at setting of “3” and takes 20 breaths per minute (the mediumflow rate):${\left( {4\quad{hr}} \right)*\frac{{.047}\quad{kg}}{{LPM}({hr})}{.72}{LPM}} = {{.135}\quad{kg}}$The mass of the batteries needed is 0.135 Kg. Assuming each battery cellis 42 g as previously stated, the number of batteries for the power packcan be calculated:${{.135}\quad{{kg}\left( \frac{1000\quad g}{1\quad{kg}} \right)}\frac{{battery}\quad{cell}}{42\quad g}} = {3.2\quad{battery}\quad{cells}}$

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention. For example, larger flow rates may beachieved by scaling the concentrator components to achieve desired flowrates at the disclosed efficiencies.

1. An oxygen concentrator comprising: an oxygen reservoir; a firstadsorbent column having an inlet, an outlet and a first bed of adsorbentmaterial; a second adsorbent column having an inlet, an outlet and asecond bed of adsorbent material; a third adsorbent column having aninlet, an outlet and a third bed of adsorbent material; an air inlet; anexhaust outlet; a vacuum pump for pumping nitrogen rich gas from one ofthe column inlets to the exhaust outlet; a product control pump forpumping oxygen rich gas from one of the column outlets to the oxygenreservoir; a control valve for controlling flow in and out of thecolumns by selectively connecting the air inlet to one column inlet,connecting the vacuum pump to another column inlet, and connecting theproduct control pump to a column outlet; a motor for driving the vacuumpump and control valve to produce vacuum swing adsorption (VSA) cyclesin which oxygen-rich product gas is separated and accumulated in thereservoir.
 2. The oxygen concentrator of claim 1 wherein the oxygenconcentrator has a volume of less than 1.0 liter.
 3. The oxygenconcentrator of claim 1 wherein the oxygen concentrator has a mass ofless than 2.3 kg.
 4. The oxygen concentrator of claim 3 wherein theoxygen concentrator has a mass of less than 1.4 kg.
 5. The oxygenconcentrator of claim 1 wherein the motor for driving includes anelectric motor.
 6. The oxygen concentrator of claim 1 wherein theadsorbent material comprises a zeolite which preferentially adsorbsnitrogen.
 7. The oxygen concentrator of claim 1 wherein the controlvalve comprises a rotary valve.
 8. The oxygen concentrator of claim 1further comprising an oxygen conserver connected to the oxygenreservoir.
 9. The oxygen concentrator of claim 1 further comprising acontrol to provide feedback control of the motor as a function of anamount of oxygen supplied from the oxygen reservoir.
 10. The oxygenconcentrator of claim 1 wherein the air inlet includes a filter.
 11. Anoxygen concentrator comprising: an ambient air inlet; an oxygenreservoir; a vacuum pump; a plurality of gas separation columnscontaining an adsorbent material that preferentially adsorbs nitrogen,each column having an inlet port at a first end and an outlet port at asecond end; a rotary valve connected to the inlet and outlet ports ofeach column for selectively connecting the columns as the valve rotatesso that during one revolution of the rotary valve each columnsequentially is in a feed phase, an evacuation phase and arepressurization phase of a vacuum swing adsorption cycle, and so thatthe columns are in different phases from one another at all times; amotor for rotating the rotary valve; and wherein during the feed phasethe rotary valve connects the ambient air inlet to the inlet port andthe oxygen reservoir to the outlet port of one of the columns; duringthe evacuation phase the rotary valve connects the vacuum pump to theinlet port of one of the columns; and during the repressurization phasethe rotary valve connects the inlet port of one of the columns to theambient air supply.
 12. The oxygen concentrator of claim 11 whereinduring a portion of the repressurization phase the rotary valve connectsa source of oxygen rich gas to the outlet port.
 13. The oxygenconcentrator of claim 11 and further comprising: means for delivering apulse of product gas from the reservoir in response to an inhalation bya patient.
 14. The oxygen concentrator of claim 11 wherein the vacuumpump is driven by the motor.
 15. The oxygen concentrator of claim 11wherein the oxygen concentrator has a volume of less than 1.0 liter. 16.The oxygen concentrator of claim 11 wherein the oxygen concentrator hasa mass of less than 2.3 kg.
 17. The oxygen concentrator of claim 11wherein the oxygen concentrator has a mass of less than 1.4 kg.
 18. Theoxygen concentrator of claim 11 wherein the total number of theplurality of columns is a multiple of three.
 19. A method of providingconcentrated oxygen product gas to a patient using an oxygenconcentrator containing a plurality of columns which separates oxygenfrom ambient air utilizing a vacuum swing adsorption process cyclecontaining a feed phase, an evacuation phase, and a repressurizationphase, wherein a different portion of the plurality of columns is indifferent phases from the other plurality of columns at all times; themethod comprising: (a) introducing ambient air into a first end of acolumn containing an adsorbent material to advance a mass transfer zonetoward a second end of the first column and to remove product gas outthe second end; (b) storing at least some of the product gas for use bythe patient; (c) drawing a vacuum on the column to remove, through thefirst end of the column, waste gas contained in the adsorbent material;and (d) repressurizing the column by introducing ambient air into theevacuated column through the first end until the column approaches 1.0atmosphere; and (e) repeating steps (a)-(d); wherein steps (a) through(e) are performed by each column of the plurality of columns.
 20. Themethod of claim 19 and further comprising: introducing an oxygen richgas into the evacuated column through the second end during step (d).21. The method of claim 19 and further comprising: delivering pulses ofstored product gas to the patient.